1. Field of the Invention
The present invention relates to a method of manufacturing dynamic random access memory (DRAM). More particularly, the present invention relates to a method of manufacturing a crown-shaped DRAM capacitor.
2. Description of the Related Art
A capacitor is a major element in a dynamic random access memory (DRAM). To reduce erroneous readings and to increase operating efficiency, capacitance of the DRAM capacitors must be increased. Capacitance of a DRAM capacitor can be increased by enlarging the effective surface area. Effective surface area can be expanded by shaping the capacitor into a crown and forming hemispherical grains (HSGs) over the capacitor surface.
The conventional method of forming a crown-shaped capacitor includes filling with photoresist, chemical-mechanical polishing (CMP) and wet etching. FIGS. 1A through 1D are schematic cross-sectional views showing the steps for producing a conventional crown-shaped DRAM capacitor. In FIG. 1A, a silicon substrate 100 after with photoresist is shown. A dielectric layer 110, a nitride layer 120, a plug 160, a patterned oxide layer 130 and a polysilicon layer 140a shaped into a crown are already formed over the silicon substrate 100 having a region 102. After filling with photoresist, the crown-shaped polysilicon layer 140a is covered by a photoresist layer 150. The photoresist layer 150 is able to resist the intrusion of slurry into the crown-shaped area during chemical-mechanical polishing.
FIG. 1B shows the structure in FIG. 1A after a chemical-mechanical polishing operation. As shown in FIG. 1B, a portion of the photoresist layer 150 and polysilicon layer 140a are removed to form an embedded crown-shaped polysilicon capacitor 140b.
FIG. 1C shows the structure in FIG. 1B after the removal of the photoresist layer 150 and the removal of the oxide layer 130 by wet etching. A crown-shaped capacitor 140b is shown above the substrate 100.
After forming the crown-shaped capacitor 140b, a layer of hemispherical grains 170 is grown over the surface of the capacitor as shown in FIG. 1D. Since the hemispherical grains can grow on the surface of the crown-shaped capacitor 140b as fast as the nitride layer 120, many hemispherical grains 170 are also formed over the nitride layer 120.
However, the aforementioned method of forming a crown-shaped capacitor has a few drawbacks. The steps involved are complicated, thereby increasing both production time and cost. In addition, selectivity of hemispherical grain growth is low. Hence, some of the hemispherical grains are likely to form over the nitride layer resulting in unwanted short-circuiting.